Smart microgrids offer a new challenging domain for power theories and compensation techniques, because they include a variety of intermittent power sources, which can have dynamic impact on power flow, voltage regulation, and distribution losses. When operating in the islanded mode, low-voltage smart microgrids can also exhibit considerable variation of amplitude and frequency of the voltage supplied to the loads, thus affecting power quality and network stability. Due to limited power capability in smart microgrids, the voltage distortion can also get worse, affecting measurement accuracy, and possibly causing tripping of protections. In such context, a reconsideration of power theories is required, since they form the basis for supply and load characterization, and accountability. A revision of control techniques for harmonic and reactive compensators is also required, because they operate in a strongly interconnected environment and must perform cooperatively to face system dynamics, ensure power quality, and limit distribution losses. This paper shows that the conservative power theory provides a suitable background to cope with smart microgrids characterization needs, and a platform for the development of cooperative control techniques for distributed switching power processors and static reactive compensators

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Smart grids offer a new challenging domain for power theories and compensation techniques, because they include a variety of intermittent power sources which can have dynamic impact on power flow, voltage regulation, and distribution losses. When operating in the islanded mode, smart micro-grids can also exhibit considerable variation of amplitude and frequency of the voltage supplied to the loads, thus affecting power quality and network stability. Due to the limited power capability of smart micro-grids, voltage distortion can also get worse, affecting measurement accuracy and possibly causing tripping of protections. In such a context, a reconsideration of power theories is required, since they form the basis for supply and load characterization and accountability. A revision of control techniques for harmonic and reactive compensators is also required, because they operate in a strongly interconnected environment and must perform cooperatively to face system dynamics, ensure power quality and limit distribution losses. This paper shows that the Conservative Power Theory (CPT) provides a suitable background to cope with smart grids characterization needs, and a platform for the development of cooperative control techniques for distributed switching power processors and static reactive compensators.

This paper proposes an effective technique to control the power flow among different phases of a three-phase four-wire distribution power system by means of single-phase converters arbitrarily connected among the phases. The aim is to enhance the power quality at the point-of-common-coupling of a microgrid, improve voltage profile through the lines, and reduce the overall distribution losses. The technique is based on a master/slave organization where the distributed single-phase converters act as slave units driven by a centralized master controller. Active, reactive, and unbalance power terms are processed by the master controller and shared proportionally among distributed energy resources to achieve the compensation target at the point-of-common-coupling. The proposed control technique is evaluated in simulation considering the model of a real urban power distribution grid under non-sinusoidal and asymmetrical voltage conditions. The main results, concerning both steady-state and transient conditions, are finally reported and discussed

The paper introduces the family of quasi-direct converters, i.e., forced-commutated adddac converters including small energy storage devices in the dc link. In particular, the case of three-phase to three-phase quasi-direct converter is considered. Since energy storage minimization calls for instantaneous inputloutput power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported.

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